Improve timers

[zfergus]

• Move timers into DescentStrategy
• Move timers into LineSearch

[codecov]

Codecov Report

Attention: Patch coverage is 98.50746% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 87.62%. Comparing base (1b142d3) to head (5705af7).

Files	Patch %	Lines
.../polysolve/nonlinear/descent_strategies/Newton.cpp	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #73      +/-   ##
==========================================
+ Coverage   87.51%   87.62%   +0.11%     
==========================================
  Files          48       48              
  Lines        2026     2045      +19     
==========================================
+ Hits         1773     1792      +19     
  Misses        253      253              

Flag	Coverage Δ
polysolve	87.62% <98.50%> (+0.11%)	⬆️

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